Preheat oven to 500 degrees F (260 degrees C). Combine soft bread crumbs, dry bread crumbs, and milk in a large bowl and allow to soak until the bread crumbs absorb most of the milk, about 10 minutes. Add ground beef, Italian sausage, 1 cup marinara sauce, eggs, garlic, Italian seasoning, and red pepper flakes and mix until thoroughly combined.